The present invention relates generally to acoustic transducers, and more specifically to a high performance ultrasonic transducer having a reduced cost of manufacture.
Ultrasonic transducers are known that may be employed in parametric speaker systems for generating sonic or ultrasonic signals in nonlinear transmission media. For example, an array of ultrasonic transducers may be employed in a parametric speaker system for generating sonic (i.e., audio) signals in air or water. A conventional parametric audio system typically includes a modulator configured to modulate an ultrasonic carrier signal with at least one audio signal, at least one driver amplifier configured to amplify the modulated carrier signal, and an ultrasonic transducer array comprising a plurality of ultrasonic transducers configured to direct the modulated and amplified carrier signal through the air along a selected path of projection. For example, the ultrasonic transducer array may comprise a plurality of self-contained electrostatic transducers, piezoelectric transducers, electrostrictive transducers, electro-thermo-mechanical film (ETMF) transducers, or polyvinylidene fluoride (PVDF) film transducers. Because of the nonlinear transmission characteristics of the air, the projected ultrasonic signal is demodulated as it passes through the air, thereby regenerating the audio signal along at least a portion of the selected projection path.
In the conventional parametric audio system, the level of audible sound produced by the system is generally proportional to the total surface area of the ultrasonic transducer array, and the coverage area of the sound generated by the array. However, this can be problematic because a typical ultrasonic transducer, such as the typical piezoelectric transducer, has a diameter of only about xc2xc inch. As a result, it is often necessary to include hundreds or even one thousand or more piezoelectric or electrostatic transducers in the ultrasonic transducer array to achieve an optimal transducer array surface area.
Although the ultrasonic transducer might be made larger to achieve higher levels of audible sound, this can also be problematic. For example, an electrostatic transducer typically includes a backplate member that is supported by a vibrator film. However, as the electrostatic transducer increases in size, the size of the backplate also increases, thereby potentially damaging the thin vibrator film supporting the larger backplate. Moreover, each of these small transducers is individually connected within the ultrasonic transducer array and typically configured to be stand-alone operable, which can significantly increase both the complexity and the cost of manufacture of the parametric audio system.
It would therefore be desirable to have an improved ultrasonic transducer that can be employed in a parametric speaker system. Such an ultrasonic transducer would provide a highly reliable and reduced cost solution to implementing an ultrasonic transducer array within the parametric speaker system.
In accordance with the present invention, an ultrasonic transducer is provided that may be employed to implement a highly reliable ultrasonic transducer array in a parametric speaker system, while reducing the cost of manufacture of the overall system. The presently disclosed ultrasonic transducer has a laminated construction that enables the formation of multiple ultrasonic transducers in the ultrasonic transducer array using a single layer of ultrasonic vibrator film, and a single matrix transducer housing.
In one embodiment, the ultrasonic transducer comprises a first insulative retaining layer, a second insulative retaining layer, and a vibrator film layer sandwiched between the first and second retaining layers. The first retaining layer includes a first plurality of apertures formed therethrough, and the second retaining layer includes a second plurality of apertures formed therethrough, in which the second plurality of apertures is substantially in registration with the first plurality of apertures. The ultrasonic transducer further comprises a first cover portion, and a second cover portion. The combination of the first retaining layer, the vibrator film layer, and the second retaining layer is sandwiched between the first and second cover portions.
In the presently disclosed embodiment, the side of the vibrator film layer facing the first retaining layer is unmetallized, and the opposite side of the vibrator film layer facing the second retaining layer is metallized. The ultrasonic transducer further includes a plurality of electrically conductive backplates and a plurality of electrically conductive springs, which are disposed between the first cover and the vibrator film layer in substantially the same plane as the first retaining layer. Each backplate is substantially in registration with a respective aperture formed through the first retaining layer, and the backplate has a shape conforming to the shape of the respective aperture. Each spring is disposed between a respective backplate and the first cover such that the spring is both mechanically and electrically connected to the respective backplate and the first cover, which has an electrically conductive surface. The first cover portion, the spring, the respective backplate, and the combination of the first retaining layer, the vibrator film layer, and the second retaining layer, are configured to cause the spring to urge the backplate against the unmetallized side of the vibrator film layer through the respective aperture.
The combination of the electrically conductive first cover, the plurality of springs, and the plurality of backplates forms a first electrode, and the metallized side of the vibrator film layer forms a second electrode. The ultrasonic transducer is configured to allow a voltage to be applied between the first and second electrodes, thereby generating an electric field between the vibrator film layer and the backplates that causes the film to be attracted to the backplates. In the event the voltage applied between the first and second electrodes is AC, the film vibrates to generate compression waves at sonic or ultrasonic frequencies corresponding to the incoming signal waveform.
In the preferred embodiment, the second cover portion includes a protective mesh layer and an ornamental cover layer, such that the protective layer is sandwiched between the second retaining layer and the ornamental layer. Further, the second retaining layer preferably has a thickness sufficient to create a spacing between the vibrator film layer and the protective and ornamental layers that reduces or effectively eliminates wave attenuation and/or absorption losses otherwise caused by the protective and ornamental layers, respectively, over a sonic or ultrasonic bandwidth of interest.
By providing an ultrasonic transducer in the above-described laminated construction that includes the single layer of ultrasonic vibrator film, an ultrasonic transducer array suitable for use in a parametric speaker system can be manufactured at a reduced cost.
Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows.